The elucidation of novel microvascular dilator mechanisms and an understanding of their role in the regulation of microvascular smooth muscle tone and blood flow are the long-range objectives of our research program. The specific focus of the research is to investigate the contribution and mechanism of action of cyclic GMP-associated, endothelium-derived relaxing factor (EDRF) and oxygen-derived species in the regulation of the cremasteric skeletal muscle microcirculation in vivo. Pentobarbital anesthetized rats will be prepared for in vivo microscopic observation and quantification of changes in arteriolar diameter in response to vasodilators, vasoconstrictors, inhibitors of prostaglandin synthesis and of EDRF, and probes designed to activate or inhibit the production of oxygen metabolites. Studies of EDRF will address the existence of this mechanism in the microcirculation, will define which vasodilator and vasoconstrictor agents stimulate its generation and will assess the possible involvement of this factor in autoregulatory processes associated with reactive hyperemia and oxygen tension induced responses. Investigations of reduced oxygen metabolites will focus on the vasomotor activities of each metabolite and the mechanism(s) responsible for their effect. The important first steps have been accomplished, namely adaptation and characterization of probes for the study of EDRF and oxygen species in the microcirculation. As these approaches have been limited previously to studies of large blood vessels in vitro, the studies presented in this proposal are significant, as they represent the first attempt to study these interrelated mechanisms in the microcirculation in vivo.